The present invention relates generally to fluid amplifiers, and more particularly to improvements in the temperature characteristics of such devices.
Fluidic devices are well known as a means for providing control functions for moving fluid streams. One type of fluidic device currently in use is the laminar proportional amplifier wherein a stream of fluid, called the supply stream, is input at an input port. The stream passes across a widened chamber, designed to prevent the stream from clinging to either of the channel walls, and arrives at a fork consisting of the two outgoing channels separated by a pointed structure called the splitter. If the power stream has not been disturbed and hits the splitter head-on, the stream will be divided in two, half of the fluid passing into one outlet channel and half into the other. As the power stream enters the system, it runs past two control jets, one on each side of the amplifier. When one of the jets is turned on and the control stream hits the supply stream with a certain pressure, it will deflect the supply stream by a certain amount. The output in the corresponding channel represents an amplification of the energy applied by the control jet, and the gain is equal to the ratio between the differential output pressure and the differential control pressure. It is necessary to specify the load conditions as this may modify the flow patterns within the device thereby altering the gain. Pressure gain is usually quoted for zero output flow and is referred to as the blocked load condition. Since the degree of the deflection of the supply stream is proportional to the pressure difference across the supply jet, the system is called a proportional amplifier. Since the flow of the supply stream through the chamber is not turbulent but is instead, laminar, the device is called a laminar proportional amplifier. The prior art has conventionally used the laminar proportional amplifier (henceforth referred to as LPA) as an analog device, serving to amplify signals through a continuum of pressures between two bounded pressure values.
The LPA operating in hydraulic fluid is limited in temperature range. Over an operating temperature range of 4.4.degree. to 70.degree. C., the kinematic viscosity of 5606 hydraulic oil changes from 40 to 7 centistoke, or about six times. This large change of viscosity presents a problem to the present LPA design because the LPA cannot operate satisfactorily over this temperature range because of variations in pressure gain within the Reynolds number range. In order to maintain the pressure gain of the LPA within an acceptable level under these conditions, temperature compensation is needed.